The present invention relates to methods and compositions for inhibiting cardiovascular cell proliferation. The invention provides methods for improving the longevity and quality of arterial grafts, for enhancing vascular NO production, and for reducing post-graft intimal hyperplasia, stenosis, and restenosis.
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Myointimal hyperplasia is a vascular response to injury that contributes to the development of vein graft disease, restenosis after angioplasty, and atherosclerosis (Motwani et al., 1998). Myointimal hyperplasia involves the migration and proliferation of vascular smooth muscle cells (VSMC) as well as the elaboration of extracellular matrix in the intima (DeMeyer et al., 1997; Kraiss et al., 1997). Vascular nitric oxide (NO), an endogenous regulator of vascular function, opposes the development of myointima formation by inhibiting VSMC proliferation and by inducing VSMC apoptosis (Cooke et al., 1997; Best et al., 1999). Failure of endogenous biological processes to control myointimal hyperplasia can lead to formation of vascular occlusions which seriously compromise tissue function.
Autologous vein grafting constitutes a major tool in coronary bypass procedures. About 400,000 to 500,000 first-time coronary graft procedures are performed every year in the United States alone. Although patient survival rates exceed 90% over the first five years after treatment, about 20% to 40% of the grafts fail during this time due to occlusive phenomena. Thus, 80,000-100,000 graft replacement procedures are needed in the U.S. yearly to avoid premature mortality. Vascular occlusive phenomena also lead to failures in other vascular grafts, such as arterial-venous anastomosis used for kidney dialysis, and in organ transplants.
In light of the significant costs to patients and insurers engendered by repeated graft procedures, there is a need to improve the longevity and quality of first-time vascular grafts. Ideally, such a procedure should be simple to carry out, without requiring extensive manipulation or lengthy processing. Furthermore, the procedure preferably involves materials that are relatively easy to prepare in therapeutically effective forms.
In one aspect, the invention provides a method for inhibiting trauma-induced intimal hyperplasia in a blood vessel. In accordance with the method, a polymer consisting of from 6 to about 30 amino acid subunits, wherein at least 50% of the subunits are arginine, and containing at least six contiguous arginine subunits, contained in a pharmaceutically acceptable vehicle, is contacted with the vessel, typically with the interior of the vessel. Such contacting is effective to reduce the level of intimal hyperplasia in and/or adjacent to the vessel, relative to the level of intimal hyperplasia that would occur in the absence of the contacting.
The hyperplasia-inducing trauma may comprise an incision to the vessel, excessive or prolonged pressure applied to the vessel, transplant of an organ containing the vessel, or a combination thereof. The contacting may occur prior to the trauma (as in preparation of a vessel segment for grafting), concurrent with, or following the trauma (as in an angioplasty procedure). The vessel may be a vessel conduit to be grafted into (as in a bypass procedure) or onto (as in an anastomosis) an endogenous vessel, or it can be an endogenous vessel receiving a graft. Also included are vein xe2x80x9cpatchesxe2x80x9d used in arterial repair. In preferred embodiments, the above noted procedures take place in a human subject.
The invention provides, for example, a method for repairing an arterial vessel site in a human subject. Accordingly, an isolated vessel conduit, such as a saphenous vein segment or an internal mammary artery segment, is contacted with a polymer as described above, in a pharmaceutically acceptable vehicle, and the vessel conduit is then grafted into a selected arterial vessel site in need of repair.
In one embodiment, the vessel is a vein which undergoes an arterial venous anastomosis procedure for the purpose of dialysis. In another embodiment, the vessel is subjected to angioplasty. In a further embodiment, the vessel is contained within a transplanted organ, such as, for example, a heart or kidney, where the contacting is preferably carried out by immersion of the organ in a solution of the polymer.
Preferably, at least 70%, and more preferably at least 90%, of the subunits in the polymer are arginine. When non-arginine subunits are present, preferably no arginine subunit is separated from another arginine subunit by more than one non-arginine subunit. The non-arginine subunits are preferably amino acid subunits which do not significantly reduce the rate of membrane transport of the polymer. In preferred embodiments, the arginine subunits are L-arginine. In particularly preferred embodiments, the polymer is an arginine homopolymer, preferably containing 7 to 15 arginine residues.
Also provided is an isolated vessel conduit, comprising, within the wall of the conduit, a polymer as described above, present at a level effective to reduce the level of post-graft intimal hyperplasia in and/or adjacent to the conduit, relative to the level of post-graft intimal hyperplasia that would occur in the absence of the polymer. The vessel conduit may be a venous or arterial segment, or it may be an artificial vessel segment made from a physiologically compatible material.
The invention also provides a method of preparing a vascular conduit for a vascular graft procedure, wherein an isolated vessel conduit, preferably the interior of the conduit, is contacted with a an arginine polymer as described above, in a pharmaceutically acceptable vehicle, for a time sufficient for the polymer to be transported into the wall of the vessel conduit to a level effective to reduce post-graft intimal hyperplasia in and/or adjacent to the conduit, relative to the level of post-graft intimal hyperplasia that would occur in the absence of such contacting with the polymer. Preferred embodiments of the polymer are as described above.
The invention also provides a method of increasing NO production in a vascular cell or tissue, by contacting a polymer consisting of from 6 to about 30 amino acid subunits, wherein at least 50% of the subunits are L-arginine, and containing at least six contiguous arginine subunits, in a pharmaceutically acceptable vehicle, with the cell or tissue.
In vascular tissue, the polymers as described above are shown to translocate through the vascular wall and into the cytoplasm and nuclei of vascular cells. In addition to their utility in inhibiting myointimal hyperplasia, the oligomers are useful as transporters of vascular therapeutics.